Apparatus capable of measuring trace substances in mixed samples in situ, conveniently and at a high sensitivity for measurement of contamination in soils and atmospheric air, inspection of residual agricultural chemicals in foods, diagnosis by circulating metabolites, urine drug screening, etc. Mass spectrometry is used as one of methods capable of measuring trace substances at high sensitivity.
A mass spectrometer ionizes substances in a gas phase by an ionization source, introduce ions into a vacuumed part, and subject them to mass analysis. For increasing the sensitivity of the mass spectrometer, improvement in a sample introduction part for efficient transportation of a sample to the ionization source is important in addition to the improvement of an ionization source, a mass analyzer, a detector, etc.
As a method of introducing a sample in a gas state into a gas chromatograph or amass spectrometer, a headspace method is used generally. The headspace method includes a static headspace method and a dynamic headspace method (refer to TrAC Trends in Analytical Chemistry, 21 (2002) 608-617).
The static headspace method is a method of injecting and tightly sealing a sample in a vial or the like while leaving a predetermined space, leaving the sample at a constant temperature till gas-liquid equilibrium is attained, and then sampling a gas present in a gas phase, that is, a headspace gas by a syringe and analyzing the same. This is a method capable of determining the quantity of a volatile substance present in a trace amount in a sample solution with less effect of a solvent in the sample solution. The concentration of the sample gas in the headspace gas can be increased, for example, by a method of overheating the sample solution to a high temperature, or by adding a salt to a sample solution thereby promoting vaporization by a salting-out effect.
The dynamic headspace method is a method of introducing an inert gas such as helium or nitrogen to a vial in which the sample has been injected and driving out the sample gas. The inert gas is introduced into the gas phase in the vial, or introduced into a liquid phase to purge the sample. When the gas is introduced into the liquid phase, since bubbles are generated, the surface area at the gas/liquid boundary is increased to further promote evaporation.
Both in the static headspace method and the dynamic headspace method, a method of concentrating the headspace gas by collection on an absorbent is also proposed.
A method of efficiently extracting a gas from a headspace part in a vial bottle has also been proposed (U.S. Pat. No. 5,869,344). In this method, a headspace gas is sucked by decreasing the pressure at the end of a pipeline on the side of an ionization source for connecting a vial bottle and an ionization source by the Venturi effect and then the gas is ionized by atmospheric pressure chemical ionization.
For promoting the evaporation of a sample, a device of dispersing a sample solution into micro droplets has also been proposed (Japanese Unexamined Patent Publication No. 2011-27557).